A total of 2,253kg of suspected cocaine with a street value of €157 million has been seized from a cargo vessel off the south-east coast.
It came as an elite unit of the Defence Forces stormed the Panamanian cargo ship in a major operation on Tuesday.
Speaking at a media briefing in Dublin on Wednesday, a senior Garda member said the discovery is the largest drug seizure in the history of the State.
Assistant Garda Commissioner Justin Kelly described the action as “hugely significant”.
Mr Kelly, from the Organised and Serious Crime Unit, said: “It shows our unrelenting determination to disrupt and dismantle networks, which are determined to bring drugs into our country.
“These groups are transnational groups. They are working all across the world and, because of that, we need to work with our international partners.”
He added: “This is a huge hit for the people involved in this.”
Investigators believe not all the drugs were destined for Ireland.
Members of the highly-trained Army Ranger Wing descended by fast-rope from a helicopter onto the ship on Tuesday, which became the focus point of a multi-agency operation which began on Friday.
The co-ordinated response from the Irish Naval Service and Army Ranger Wing also involved customs officers and the Garda national drugs and organised crime unit.
The agencies said the seized MV Matthew is a Panamanian-registered bulk cargo vessel originating in South America.
It was intercepted by the Army Ranger Wing and detained in the early hours of Tuesday.
The elite unit boarded the ship after the Naval Service’s patrol vessel, the LE William Butler Yeats, fired warning shots in its direction.
Two helicopters and two planes were also involved in the operation.
The Air Corps and Naval Service had been tracking the container ship over a number of days.
By David Young and Cillian Sherlock, PA
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